Heat pump with improved performance during cold outdoor temperatures

ABSTRACT

A heat pump system that achieves improved performance in cold weather by slowing the indoor blower motor in response to reduced temperature or pressure of the indoor liquid refrigerant line is described. A pressure transducer or temperature sensor on the indoor refrigerant line sends an electrical signal to a variable speed drive controlling the indoor blower motor, so that the indoor blower motor maintains normal speed during cooling or defrosting mode. The signal input from the pressure transducer or temperature sensor commands the variable frequency drive control to slow the fan motor down or speed it up by modifying the voltage and the frequency to the indoor motor. As a result, the indoor air handler motor slows down or speeds up to maintain the head pressure at optimal performance.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application relies on the disclosure of and claims priority to and the benefit of the filing date of U.S. Provisional Application No. 61/978,316, filed Apr. 11, 2014, the disclosure of which is hereby incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of heat pumps. More particularly, the present invention relates to an improved heat pump system which includes an indoor blower motor controlled by a variable frequency drive in operable connection with a pressure or temperature sensor which sends an electrical signal to the variable frequency drive to slow the indoor blower motor down in response to increased refrigerant pressure or temperature.

2. Description of Related Art

Commercial and residential heat pumps have had an enduring problem of reduced performance during heating mode at cold temperatures. Typically, as the temperature falls outside, it becomes increasingly more difficult for the heat pump to extract heat from the colder outdoor air. Head pressure drops as well, and therefore a typical heat pump system will suffer reduced performance. The most common result of this is “cold blow”, which results in the indoor fan blowing air at uncomfortable low temperatures. A number of attempts have been made to address this and related issues, including those described in U.S. Pat. Nos. 5,782,101; 7,340,910; 5,036,676; 6,282,910; 5,081,846; and 5,247,805, and U.S. Patent Application Publication Nos. 2004/0261441 and 2011/0125328, each of which is hereby incorporated by reference herein in its entirety. However, despite these efforts, there remains a need for heat pump systems that operate more efficiently during heating mode in cold weather.

SUMMARY OF THE INVENTION

The present disclosure describes a heat pump system that achieves improved performance in cold weather by slowing the indoor blower motor in response to increased temperature or pressure of the indoor liquid refrigerant line. In embodiments, a pressure transducer or temperature sensor on the indoor refrigerant line sends an electrical signal to a variable speed drive (also known as a variable frequency drive; “variable speed drive” and “variable frequency drive” may be used interchangeably herein) controlling the indoor blower motor. Additionally, the variable speed drive and/or the reversing valve may receive an electrical signal from a thermostat so that the indoor blower motor maintains normal speed during cooling or defrosting mode. The pressure transducer or temperature sensor mounted on the liquid line at the indoor air handler coil sends an electrical signal input to the variable frequency drive control which will slow the fan motor down or speed it up by modifying the voltage and the frequency to the indoor motor. As a result, the indoor air handler motor slows down or speeds up to maintain the head pressure at optimal performance. By slowing down the indoor blower motor in the present system during cold outdoor temperatures, the head pressure will be maintained which will raise the discharge temperature coming out of the vents from the indoor blower. As the outside temperature falls, the variable speed drive and indoor motor will maintain the optimal head pressure thereby increasing the temperature coming out of the air vents and resulting in a more efficient system which saves energy.

In one embodiment, the present disclosure provides a heat pump system having an indoor coil and an outdoor coil connected to each other in a circuit through a fluid line (which can include hot gas lines and/or liquid lines) and through a compressor operably connected to a reversing valve so the flow of fluid (may also be referred to as a refrigerant) can be moved by the compressor in either direction through the circuit, and further having an indoor blower motor configured to blow air across the indoor coil. In portions of the system, during use, the fluid moving through the system can be a gas or liquid. The heat pump system may comprise a variable speed drive in operable connection with the indoor blower motor and a sensor configured for measuring pressure or temperature of an indoor portion of the fluid line (also referred to as a refrigerant line). The sensor may be operably connected to send an electrical signal to the variable speed drive and the variable speed drive may be operably configured to send a reduced electrical signal to the indoor blower motor in response to a reduced electrical signal from the sensor thereby reducing the indoor blower motor speed.

In another embodiment, the present disclosure provides a method of operating a heat pump system having an indoor coil and an outdoor coil connected to each other in a circuit through a refrigerant line and through a compressor operably connected to a reversing valve so the flow of refrigerant can be moved by the compressor in either direction through the circuit, and further having an indoor blower motor configured to blow air across the indoor coil. The method may comprise providing a variable speed drive, connecting the variable speed drive to the indoor blower motor, measuring the pressure or temperature of an indoor portion of the refrigerant line, and in response to reduced pressure or temperature over a period of measurement, sending a reduced electrical signal from the variable speed drive to the indoor blower motor, thereby slowing the indoor blower motor. In another embodiment, a control board controlled by a pressure transducer or temperature sensor may be used to slow the indoor single phase motor down.

In another embodiment, the present disclosure provides a heat pump system comprising an indoor coil and an outdoor coil connected together in a circuit, one side of the indoor coil connected to one side of the outdoor coil through a refrigerant line, and the opposite side of each coil connected to a compressor through a reversing valve so the flow of refrigerant can be moved by the compressor in either direction through the circuit. The heat pump system may further comprise a three-phase indoor blower motor configured to blow air across the indoor coil, a variable speed drive with a three-phase output in operable connection with the indoor blower motor, and a sensor configured for measuring pressure or temperature of an indoor portion of the refrigerant line. The sensor may be configured to send an electrical signal to the variable speed drive during cooling mode. The variable speed drive may be operably configured to send an electrical signal that is reduced in voltage or hertz to the indoor blower motor during heating mode in response to a reduced electrical signal from the sensor, thereby reducing the indoor blower motor speed. Further, the variable speed drive may be configured to operate the indoor blower motor at full speed during cooling mode in response to the electrical signal from a thermostat.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawing illustrates aspects of embodiments of the present invention, and should not be used to limit or define the invention. Together with the written description the drawing serves to explain certain principles of the invention.

FIG. 1 is a schematic diagram showing an embodiment of a heat pump system of the present disclosure having a variable speed drive with a three-phase input and three-phase output connected to the indoor blower motor.

FIG. 2 is a schematic diagram showing an embodiment of a heat pump system of the present disclosure having a variable speed drive with a three-phase input and one-phase output connected to the indoor blower motor.

FIG. 3 is a schematic diagram showing an embodiment of a heat pump system of the present disclosure having a variable speed drive with a one-phase input and three-phase output connected to the indoor blower motor.

FIG. 4 is a table of results of testing of a prototype of the invention.

FIG. 5 is a graph showing the relationship between indoor blower motor speed and outdoor temperature during testing of the prototype of the invention.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS OF THE INVENTION

Reference will now be made in detail to various exemplary embodiments of the invention. It is to be understood that the following discussion of exemplary embodiments is not intended as a limitation on the invention. Rather, the following discussion is provided to give the reader a more detailed understanding of certain aspects and features of the invention.

FIGS. 1-3 show various embodiments of systems 10, 10B, 10C of the invention. Referring now to FIG. 1, an exemplary embodiment of a heat pump system 10 of the present disclosure operating in heating mode is shown, with the vertical dashed line in the center of the figure showing the boundary between indoor components (left) and outdoor components (right). Heat pump system 10 includes an indoor heat exchanger or coil 12 and an outdoor heat exchanger or coil 14. One side of the indoor coil 12 is connected to one side of the outdoor coil 14 through a liquid line 16, and the opposite side of each coil is connected to a compressor 40 to complete a circuit. Compressor 40 includes or is operably connected to a reversing valve 38 so the flow of refrigerant can be moved by the compressor 40 in either direction through the circuit. Liquid line 16 may include an indoor thermal expansion valve 23 and/or an outdoor thermal expansion valve 25. A bypass valve (not shown) may route coolant to bypass each of the thermal expansion valves.

When the heat pump system 10 is operating in heating mode as shown in FIG. 1, the compressor 40 directs hot compressed vapor through indoor hot gas line 20 to the inside coil 12 as shown by the arrow leading from compressor 40. Indoor coil 12 acts as a condenser and releases heat energy as air is blown across it by indoor fan 42 (thereby blowing heated air 62), while liquid line 16 exiting the indoor coil 12 is directed to the outside coil 14, which acts as an evaporator and stores heat energy as the outdoor fan 44 blows air across it (thereby blowing cooled air 64). Refrigerant exits the outdoor coil 14 as vapor 18 which is then directed to the compressor 40 through the reversing valve 38. When the heat pump is operating in cooling mode (not shown), the roles of the indoor coil 12 and outdoor coil 14 are reversed.

The system 10 further comprises a pressure transducer 30 (or alternatively a temperature sensor) located on the indoor liquid line 16 proximal to the indoor heating coil 12. The pressure transducer 30 or temperature sensor produces an electrical signal output 59 that is received by a variable speed drive 50. In an exemplary embodiment, the variable speed drive 50 has a three-phase input 55 and a three-phase output 53 which is connected to the three-phase indoor fan motor 32. However, the system 10B of FIG. 2 shows that the variable speed drive 50B can have a three-phase input 55 and one-phase output 53B in embodiments in which the indoor fan motor is a one-phase motor 32B and/or the variable speed drive 50C can have a one-phase input 55B and a three-phase output 53 as shown in FIG. 3. The variable speed drive 50, 50B, 50C and/or the reversing valve 38 can receive an electrical signal input 57 from a thermostat 70. The variable speed drive 50, 50B, 50C is configured to slow the indoor fan motor 32 down only during the heating cycle by receiving an electrical signal from a thermostat 70 of the heat pump system 10, 10B, 10C so that the indoor blower motor 32 operates at a normal speed and operation in air condition mode or defrost cycle. The outdoor fan 44 has a separate motor 34 which operates independently of the indoor fan motor 32.

The system achieves improved performance by including the pressure transducer 30 or temperature sensor on the liquid line 16 coupled to the variable speed drive 50, 50B, 50C which controls an indoor fan motor 32 that is configured to take a drop in voltage/hertz. This configuration allows the heat pump system to reduce the speed of the indoor blower motor based on feedback (pressure or temperature sensing) from the liquid line 16 exiting the indoor coil 12. However, in other embodiments, the pressure or temperature sensor 30 may be placed on the hot gas line 20 entering the indoor coil 12. The indoor motor may be a three-phase motor 32 as shown in FIG. 1 and FIG. 3, or alternatively may be a one-phase motor 32B as shown in FIG. 2. The indoor motor 32, 32B may be on the indoor air handler for a split system heat pump/package unit such as those used for residential and commercial heat pumps.

In an exemplary embodiment, the pressure transducer 30 may send an input signal 59 ranging from 4-20 milliamp or alternatively 0-10 volts DC to the variable frequency drive 50. However, these amperages and voltages are merely exemplary, and any suitable amperage or voltage may be used in the signal from the sensor as long as the current or voltage of the signal from the sensor correlates or is associated with the pressure or temperature of refrigerant in the indoor portion of the refrigerant line. Further, in an exemplary embodiment, the variable speed drive 50, 50B, 50C and/or the reversing valve 38 may receive a 24 volt signal 57 from a thermostat 70. However, any suitable voltage or current signal may be used as the electrical signal from the thermostat 70.

In an exemplary embodiment, the pressure transducer 30 reads the operating pressure of the liquid in the indoor liquid line 16 and the variable speed drive 50, 50B, 50C may keep the heat pump system at a head pressure of 300 psi to 370 psi (and preferably 335 psi) during the whole cycle of the call for heat by controlling the speed of the indoor blower fan motor such that the indoor blower motor 32 is slowed down during colder temperatures, thereby maintaining the head pressure. In another embodiment, a control board (not shown) controlled by the pressure transducer 30 is used to slow the indoor motor down.

In an exemplary embodiment, the heat pump system uses chlorodifluoromethane, or R22 refrigerant. However, in another exemplary embodiment, the heat pump system uses 410A refrigerant (a mixture of difluoromethane and pentafluoroethane). However, in other embodiments, the heat pump may use any suitable hydrofluorocarbon, hydrochlorofluorocarbon, hydrocarbon, alkyl halide, or other gas refrigerant, or combinations of any of the above-mentioned refrigerants.

On relatively warmer days (e.g. about 40° F. or higher outside), but cold enough for using the heat pump system of the present disclosure in heating mode, the pressure transducer or temperature sensor coupled with the variable frequency drive will have the motor running at full speed (normal operation). On relatively colder days (e.g. below about 40° F. outside), the present heat pump system will produce better heat in heating mode by running the indoor blower motor at reduced speed (cold temperature operation). Normal temperature of discharged air out of indoor air vents from the indoor blower in a conventional heat pump system is about 80-90° F. With the system of the present disclosure, the temperature of the discharged air may be in the range of about 5° to about 10° F., about 5° to about 15° F., or even about 5° to about 20° F. warmer coming out of the indoor vents compared to a conventional system, depending on how cold the temperature is outside. The colder the outside temperature is below 40° F., the greater warming of the air coming out of the vents due to the indoor blower motor slowing down. By slowing down the indoor blower motor in the present system, the head pressure will be maintained which will raise the discharge temperature coming out of the vents from the indoor blower. As a result, the heat pump system of the present disclosure achieves less time for the heat pump to actually stay on and less time for electric heating elements to have to come on, thereby saving a significant amount of money for electricity during the heating season.

Another embodiment of the present disclosure is a method for installing a heat pump system or retro-fit kit of the present disclosure. The method may comprise:

installing a variable frequency drive on the indoor air handler in the electrical section;

installing a motor in the squirrel cage and blower housing in the indoor air handler unit that is configured to take a drop in voltage and hertz; and

installing a pressure transducer or temperature sensor on the liquid line and connecting the output to the variable frequency drive.

The method may further optionally comprise providing an input from the reversing valve wires so that the indoor blower is able to operate at full speed during cooling or defrost mode and only slows down during heating mode.

The pressure transducer or temperature sensor may output a 4-20 milliamp or a 0-10 volts DC signal to the variable speed drive or a control board to control the indoor blower motor by speeding it up or slowing it down. The method allows the indoor blower motor to slow down or speed up through input from the variable frequency drive or control board controlling it.

Embodiments of the invention include a retro-fit kit comprising one or more components of the heat pump systems described in this disclosure, wherein the components are operably configured for adapting an existing heat pump system into a heat pump system provided by the invention. In the context of this disclosure, a retro-fit kit is a compilation of one or more heat pump system components that can be used to update an old heat pump system into a heat pump system of the invention. For example, such a retrofit kit can be used to improve the efficiency of an existing heat pump system by retrofitting the existing system with a variable speed drive operably configured to send a reduced electrical signal to the blower motor in response to a reduced electrical signal from the sensor, thereby reducing the indoor blower motor speed and as a result outputting higher temperature heat.

Also included within the scope of the invention is a kit for converting a heat pump system into a higher efficiency heat pump system, the kit comprising:

a control board or a variable speed drive operably configured for connection with an indoor blower motor of a heat pump; and

a sensor configured for measuring pressure or temperature of an indoor portion of a refrigerant line of the heat pump;

wherein the sensor is operably configured to send an electrical signal to the variable speed drive; and

wherein the variable speed drive is operably configured to send a reduced electrical signal to the blower motor in response to a reduced electrical signal from the sensor thereby reducing the indoor blower motor speed.

EXAMPLE 1

A test was conducted with the electric heat unhooked on a R22 heat pump system when it was 18° F. outside. The thermostat was set to 75° F. to call for heat. The system was run for 10 minutes and it was discharging 90° F. air out of the supply vents with a 70° F. return air temperature. Refrigerant gauges were hooked to the outdoor unit and registered a 31 psi suction and 185 psi head pressure. The system was turned off and a low ambient control was hooked up, which is used to slow down a condenser motor on outdoor AC units or other HVAC equipment to keep the refrigerant head pressure up in cold outdoor temperatures. The low ambient control was installed on an indoor air handler unit and wired to slow down the indoor motor. Further, a temperature sensor was strapped to the liquid line and the thermostat was set to 75° F., calling for heat. It was 18° F. outside and 70° F. at the return filter grill. When the heat pump came on, the control slowed down the indoor motor and maintained 215 psi head pressure and still 31 psi suction pressure on the R22 heat pump. After running for 10 minutes, it was discharging 101° F. air out of the air vents, which was 11° F. warmer than before the motor was slowed down. In addition, the heat pump system was checked the same way on another day, when the outdoor temperature was 29° F., and a discharge of 104° F. supply air with a 70° F. return air was observed.

EXAMPLE 2

More extensive testing on a prototype of the invention was done on a two ton Heil 410A—13 Seer Heat Pump over several days. The results of testing the prototype are shown in the table of FIG. 4. All temperatures are measured in Fahrenheit. The supply air temperature before testing on Dec. 18, 2014 was 96.3° F. and was approximately 90-96° F. on other days. During testing, the supply air temperature ranged from 101° F. to 106.3° F. at outdoor temperatures ranging from 25° F. to 35° F. The supply air temperature cooled to 93° F. at an outdoor temperature of 8° F., which may have been due to limitations in the heat exchange capacity of the refrigerant at that temperature.

FIG. 5 is a graph showing indoor blower motor speed decreased with decreasing outdoor temperatures as a result of testing the prototype. The relationship was approximately linear, with a correlation coefficient of 0.94. The graph shows proof-of-principle of the ability of the prototype to slow the indoor blower motor in response to decreased outdoor temperatures and to increase supply air temperature, thereby increasing heat pump efficiency.

The present invention has been described with reference to particular embodiments having various features. In light of the disclosure provided above, it will be apparent to those skilled in the art that various modifications and variations can be made in the practice of the present invention without departing from the scope or spirit of the invention. One skilled in the art will recognize that the disclosed features may be used singularly, in any combination, or omitted based on the requirements and specifications of a given application or design. Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention.

It is noted in particular that where a range of values is provided in this specification, each value between the upper and lower limits of that range is also specifically disclosed. The upper and lower limits of these smaller ranges may independently be included or excluded in the range as well. The singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. It is intended that the specification and examples be considered as exemplary in nature and that variations that do not depart from the essence of the invention fall within the scope of the invention. Further, all of the references cited in this disclosure are each individually incorporated by reference herein in their entireties and as such are intended to provide an efficient way of supplementing the enabling disclosure of this invention as well as provide background detailing the level of ordinary skill in the art. 

1. A heat pump system comprising: a compressor; an indoor coil and an outdoor coil connected to the compressor and connected to each other in a circuit by way of a liquid line comprising a liquid; a reversing valve connected with the liquid line for reversing flow of the liquid; an indoor blower motor configured to blow air across the indoor coil; a variable speed drive in operable connection with the indoor blower motor; and a sensor configured for measuring pressure or temperature of the liquid in an indoor portion of the liquid line; wherein the sensor is operably configured to send an electrical signal to the variable speed drive; and wherein the variable speed drive is operably configured to send a reduced electrical signal to the blower motor in response to a reduced electrical signal from the sensor thereby reducing speed of the indoor blower motor.
 2. The system of claim 1, wherein the variable speed drive is operably configured to send an electrical signal to the indoor blower motor that is reduced in voltage or hertz in response to a reduced electrical signal from the sensor.
 3. The system of claim 1 further comprising a thermostat operably configured to send an electrical signal to the variable speed drive during cooling mode.
 4. The system of claim 3, wherein the variable speed drive is configured to operate the indoor blower motor at full speed during cooling mode in response to the electrical signal from the thermostat.
 5. The system of claim 4, wherein the thermostat is operably configured to send a 24 volt signal to the variable speed drive during cooling mode.
 6. The system of claim 1, wherein the sensor is operably configured to send a 4 to 20 milliamp or 0 to 10 volts DC signal to the variable speed drive.
 7. The system of claim 6, wherein the signal from the sensor is proportional to pressure or temperature level of refrigerant in the indoor portion of the liquid line.
 8. The system of claim 1, wherein the indoor blower motor is a three-phase motor.
 9. The system of claim 1, wherein the indoor blower motor is a one-phase motor.
 10. A method of operating a heat pump system, the method comprising: providing a variable speed drive and connecting the variable speed drive to an indoor blower motor of a heat pump; measuring pressure or temperature of a liquid in an indoor portion of a liquid line connecting an indoor coil, an outdoor coil, and a compressor of the heat pump; and in response to reduced pressure or temperature over a period of measurement, sending a reduced electrical signal from the variable speed drive to the indoor blower motor, thereby slowing speed of the indoor blower motor.
 11. The method of claim 10, wherein the reduced electrical signal from the variable speed drive is reduced in voltage or hertz.
 12. The method of claim 10 further comprising sending an electrical signal to the variable speed drive during cooling mode.
 13. The method of claim 12 further comprising operating the indoor blower motor at full speed during cooling mode in response to the electrical signal.
 14. The method of claim 13 further comprising sending a 24 volt signal to the variable speed drive during cooling mode.
 15. The method of claim 10 further comprising sending a 4 to 20 milliamps or a 0 to 10 volt DC signal to the variable speed drive.
 16. The method of claim 15, wherein the signal is proportional to pressure or temperature of the liquid in the indoor portion of the liquid line.
 17. The method of claim 10, wherein the indoor blower motor speed correlates with outdoor temperature such that the indoor blower motor speed is reduced as the outdoor temperature is reduced.
 18. A kit for converting a heat pump system into a higher efficiency heat pump system, the kit comprising: a control board or a variable speed drive operably configured for connection with an indoor blower motor of a heat pump; and a sensor configured for measuring pressure or temperature of a fluid in an indoor portion of a liquid line of the heat pump; wherein the sensor is operably configured to send an electrical signal to the variable speed drive; and wherein the variable speed drive is operably configured to send a reduced electrical signal to the blower motor in response to a reduced electrical signal from the sensor thereby reducing speed of the indoor blower motor. 